There is an increasing need for new materials that are both biocompatible and biodegradable for medical use, particularly for drug delivery, therapeutic devices and gene therapy/delivery. Particularly common materials for such applications have been degradable polymers such as polyesters, including poly (L-lactic acid), poly(glycolic acid), and poly(lactic-co-glycolic acid). See Duncan, R.; Ringsdorf, H.; Satchi-Fainaro, R. Adv. Poly. Sci. 2006, 192, 1-8; and Finne-Wistrand, A.; Albertson, A.-C. Annu. Rev. Mater. Res. 2006, 36, 369-395 both incorporated herein by reference. However, these polyesters lack many properties necessary for medical applications, and undergo homogeneous, bulk degradation which is detrimental to the long-term mechanical properties of the material. Degradation rates can also be quite slow—from several months to years. Furthermore, their crystallinity leads to hard materials that deform upon degradation. In contrast, surface eroding polymers, such as polyanhydrides, maintain their mechanical integrity during degradation and exhibit a gradual loss in size. See Gopferich, A.; Tessmar, J. Adv. Drug Deily. Rev. 2002, 54, 911-931; Katti, D. S.; Lakshmi, S.; Langer, R.; Laurencin, C. T. Adv. Drug Deily. Rev. 2002, 54, 933-961; and Kumar, N.; Langer, R.; Domb, A. J. Adv. Drug Deliv. Rev. 2002, 54, 889-91 all hereby incorporated herein by reference.